Compared with traditional 2-D flat panel display technology, 3-D display technology is able to present more vivid stereoscopic images, such that it becomes one of important developing directions of current display technologies. At present, the most popular 3-D imaging technology is shutter glasses technology. The principle of this technology is to alternately turn on and turn off left-eye lens and right-eye lens of 3-D glasses in order, as shown in FIG. 1: when the right-eye lens is on, the screen outputs an image for the right eye in the same time; when the left-eye lens is on, the screen outputs an image for the left eye in the same time, and then based on view angel difference between the left and right eyes, the viewers may synthesize images from the left eye and right eye to a 3-D image with depth of field and hierarchical perception.
At present, the liquid crystal display device has become the major appliance for displaying in every industries even family entertainment due to its advantages of slim exterior, low power consumption and radiation-free. Therefore, a 3-D imaging liquid crystal display with shutter glasses technology has also become a new hot spot. The operation principle of the liquid crystal display device is to achieve image display of different grey scales by changing the rotation angle of liquid crystal molecules. If driven by direct current mode, mobile ions in the liquid crystal material may move to transparent conductive film ITO in a same direction under influence of electric field, and this polarization phenomenon may produce another electric field within the panel and thereby interfere the rotation direction of the liquid crystal molecules, such that a phenomenon of direct current residue may appear. In order to avoid effect of direct current residue on image displaying quality, alternating current drive mode is usually adopted to the liquid crystal panel. The specific implementing manner is to periodically change the voltage acting on a pixel electrode of a pixel unit by changing polarity of a data signal with image information.
An example is taken by polarity inversion driving method of single-frame image shown in FIG. 2, it is assumed that there is such a liquid crystal display device of 256 grey scales, of which transparent white screen (white screen of 255 scales) is marked as L255and opaque dark screen (black screen of 0 scale) is marked as L0, wherein positive and negative polarity driving voltages for the white screen are 7V and 5V respectively, and positive and negative polarity driving voltages for the black screen are 1V and 11V respectively, and the common electrode voltage is 6 v. Then, variation in the voltage of a certain pixel electrode (or a sub-pixel electrode) and its voltage difference from the common electrode may be shown as TABLE 1.
TABLE 1
As shown in TABLE 1, under this situation, the voltage difference on the pixel electrode relative to the common electrode alternatively changes between 1 V and 5 V. That is, the voltage acting on liquid crystal molecules during the positive polarity driving period is 1V, while voltage acting on liquid crystal molecules during the negative polarity driving period is 5 V. Since the voltage difference acting on liquid crystal molecules between the positive and negative polarity driving periods is always present as positive and is too large to be counteracted, there would be electricity charge residue caused, similar to the direct current residue, after a long time operation, such that 3-D imaging residue may appear. In the prior art, in order to eliminate the 3-D imaging residue mentioned above, a method for polarity inversion of multi-frame images is adopted. As shown in FIG. 3, an example is taken by double-frame image polarity inversion method. In this method, because the polarity of a data signal is switched over every two frames, in one hand, it provides much more time to charge for a certain pixel electrode (or sub-pixel electrode) in the liquid crystal panel to reach a predetermined voltage level more easily. In other hand, variation in the voltage of the pixel electrode and its voltage difference from the common electrode is shown as TABLE 2.
TABLE 2
As shown in TABLE 2, under this situation, the voltage difference on the pixel electrode relative to the common electrode repeatedly switches in the cycle of 1V→−5V−1V→5V. That is, voltages acting on liquid crystal molecules during the positive polarity driving period are 1V and −5V, while voltages acting on liquid crystal molecules during the negative polarity driving period are −1V and 5V. Voltage differences on the pixel electrode from the common electrode during the positive and negative polarity driving periods counteract one another, thus the imaging residue may be avoided. However, another problem is derived in this condition, which is brightness difference between the right-eye images and the left-eye images. This phenomenon is more conspicuous for the liquid crystal panel using charge sharing technology to improve color shift. That is because that each pixel unit of the liquid crystal display panel using sharing charge technology is provided with a sharing capacitor to redistribute the charge in a main area and a sub area of the pixel electrode under the action of a control signal. The sharing capacitor has a capability to store the charge. When polarity of the charge obtained by the sharing capacitor during a new frame of image is same with the charge stored during the previous frame of image, the image is brighter because of charge accumulation; otherwise, when polarity of the charge obtained by the sharing capacitor during a new frame is opposite to the charge stored during the previous frame, the image is darker because of charge counteraction. Therefore, for the same data signal input, such as L255 shown in TABLE 3, brightness in the left-eye images is always weaker than that of the right-eye images while output by the liquid crystal display panel based on the double-frame polarity inversion method.
TABLE 3TimeTime1st2nd3rd4th5th6th7th8th9thAxisframeframeframeframeframeframeframeframeframe. . .InputL255L255L255L255L255L255L255L255L255. . .SignalL/RLRLRLRLRL. . .Polarity++−−++−−+. . .BrightnessDarklightDarklightDarklightDarklightDarklight
To solve the problem mentioned above, with numbers of repeated experiments and years of research and designing in 3-D imaging technology for liquid crystal display panels, the inventor of this present invention proposes a new driving method for polarity inversion of data signals and a corresponding image displaying method for the liquid crystal panel, which are not only able to eliminate 3-D imaging residue but also improve lightness difference between the right-eye images and the left-eye images.